Removal of sulfur oxides and particulate matter from waste gas streams

ABSTRACT

A process for the removal of particulate matter and sulfur oxides from waste gases is disclosed which comprises cross-current contacting of the waste gas stream with a moving bed of supported, copper-containing acceptor in a first zone, thereby accepting the sulfur oxides and filtering out the particulate matter, removing in subsequent separate zones the particulate matter and the sulfur oxides from the acceptor and, optionally, reactivating the acceptor in a subsequent zone before introducing it back into the first zone for further removal of sulfur oxides and particulate matter. An apparatus suitable for carrying out the process is also described.

BACKGROUND OF THE INVENTION

This invention relates to a process for the removal of particulatematter and sulfur oxides from waste gases such as flue gas. Theinvention also relates to an apparatus for carrying out such a process.

Because of increasingly stringent requirements on the abatement of airpollution, the removal of sulfur oxides from gas mixtures, in particularfrom hot waste gases containing relatively small amounts of sulfuroxides, such as flue gases and gases originating from roastingprocesses, has in the past few years become of great concern andtechnical importance.

In many cases these waste gases also contain particulate matter, inparticular when they emerge from roasting processes or from electricalpower plants (coal-fired and sometimes oil-fired ones), which must alsobe removed from the waste gases. It is possible to remove theparticulate matter, which, generally, consists of small particles and iscalled "fly ash", from the waste gases before or after the removal ofthe sulfur oxides, e.g., buy filtration, with cyclones or byelectrostatical precipitation. Such measures, however, require largecapital investment in addition to the capitol cost of the separatefacilities for sulfur oxide removal. Further, even with this very largecapitol investment there is no assurance of complete success since thestate of the art on particulate matter removal is not sufficientlyadvanced to assure trouble-free operation in all instances.

Accordingly, it would be very desirable if a process could be developedfor the removal of both particulate matter and sulfur oxides from wastegases, in which there is no need for costly separate installations forthe removal of particulate matter.

SUMMARY OF THE INVENTION

It has now been found that supported, copper-containing acceptors forsulfur oxides will function very effectively to remove both sulfuroxides and particulate matter from waste gases in the same processingzone under reaction conditions required for sulfur oxide acceptanceprovided such acceptors are employed in particulate form in a moving bedwhich contacts the waste gas stream in cross-current fashion. Further,it has also been found that copper-containing acceptors which are loadedwith sulfur oxides and particulate matter by this cross-currentcontacting procedure can be readily processed into a reuseable from bypassing the loaded acceptor through separate zones for removal of theparticulate matter and the sulfur oxides, with final activation of thesulfur oxide acceptance sites being carried out in situ in the sulfuroxide and particulate matter removal zone or, optionally, in anadditional separate zone positioned subsequent to the removal zones.Accordingly, the instant invention provides a process for the removal ofsulfur oxides and particulate matter from waste gases containing samewhich comprises

A. contacting the waste gas stream under oxidative conditions in asulfur oxide and particulate matter removal zone with a solid acceptorcomprising copper or copper compound or mixtures thereof supported on aparticulate carrier, said contact being established by passing the wastegas at a temperature of from about 300° to 500°C cross-currently througha moving bed of the solid acceptor, thereby accepting the sulfur oxideon said acceptor filtering out the particulate matter to afford anacceptor loaded with sulfur oxides and particulate matter and a wastegas stream substantially free of both sulfur oxides and particulatematter;

B. removing the particulate matter from the loaded acceptor in a firstseparation zone wherein the acceptor loaded with both sulfur oxides andparticulate matter is stripped of particulate matter by transporting theloaded acceptor through a stream of an inert stripping gas;

C. separating the sulfur oxides from the acceptor product of the firstseparation zone by contacting the acceptor with a reducing gas at atemperature between 300°-500°C in a second separation zone whereby thesulfur oxides bound to the acceptor are released as SO₂ gas and

D. returning the acceptor product of the second separation zone intocross-current contact with said waste gases under oxidative conditionsin the sulfur oxide and particulate matter removal zone. In analternative aspect of the process of the invention, the acceptor productof the second separation zone from which sulfur oxides have at leastpartly, and in most cases substantially completely been removed, isreactivated by contacting it with an oxidizing agent, preferably anoxygen-containing gas, in an activation zone before its introductioninto the sulfur oxide and particulate matter removal zone.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the first zone the supported, copper-containing acceptor is to bebrought into intimate contact with the waste gas to be treated, bypassing the waste gas cross-currently through a moving bed of acceptorparticles. By the employment of this contacting technique it has beenfound that essentially complete trapping of the particulate matter canbe accomplished such that little or no particulate matter passes themoving acceptor bed while at the same time maintaining the effectivenessof the acceptor to contact and absorb the sulfur oxides present in thewaste gas. This finding is surprising since previously it has beenconsidered impossible under pratical conditions to even employ a movingor fluidized bed of acceptor particles to remove SO₂ from gas streamscontaining particulate matter because of the clogging off of sulfuroxide acceptance sites by trapped particulate matter. However, the useof the cross-current contacting technique of the instant inventionapparently limits the rate of fly ash and/or other particulate materialdeposition on the acceptor such that the acceptor is able to contact andaccept substantially all of the sulfur oxides present in the waste gasprior to its becoming clogged off with particulate matter. Thus, theemployment of the cross-current contacting prodecure of the inventionplaces an inherent limitation on the intimacy of contact between thewaste gas and the moving acceptor bed which allows substantiallycomplete acceptance of sulfur oxides and trapping of particulate matterto occur in the same processing operation. Of course, the extent ofcross-current contact between the waste gas and the moving acceptor bedwill vary widely depending on the type of waste gas which is beingtreated since the concentrations of both the sulfur oxides and theparticulate matter relative to the total gas make-up and to each otherwill bear on the degree of cross-current contacting required to effectthe desired removal. One skilled in the art will recognize that theproper degree of cross-current contacting can be readily ascertained inany given case by merely analyzing the product of the cross-currentcontacting procedure for sulfur oxides and particulate matter andvarying process conditions, i.e., waste gas flow rate, moving bedvelocity, density and thickness, etc., until the desired removal orsulfur oxides and particulate matter is achieved. For typical sulfuroxides and particulate matter-containing waste gases such as flue gaswhich generally contain relatively low concentrations, i.e., 0.1-5% v,of sulfur oxides and small quantities of particulate matter, i.e., 1-20g per nm³ of waste gas, it is preferred for practical reasons that thelayer of the acceptor material to be passed by the waste gas betweenabout 25 and 100 cm thick. Under these conditions removal of sulfuroxides and particulate matter can be effected by passing the waste gasstream at a velocity of between about 1 m/sec and 7 m/sec intocross-current contact with the moving acceptor bed flowing at a rate ofabout 0.4 mm/sec to about 2.5 mm/sec; the specific velocities chosenbeing dependent on the thickness of acceptor layer employed.

The acceptor is very suitably used in the form of granules, spheres,pellets or the like, with diameters in the 1-5 mm range. The particulatematter in the waste gas, the particles of which generally have adiameter below 0.2 mm, or even below 0.5 mm, is readily filtered by theacceptor during the contact with the waste gas. If desired, part of theparticulate matter (in particular the bigger particles) may be removedfrom the waste gas with a simple apparatus (e.g., a cyclone) prior tothe contact of the waste gas with the acceptor in the first zone.

The acceptor should have a high mechanical strength in order to avoidthe formation of a significant amount of small particles (fines) thereofby attrition during transport of the acceptor through the zones. It ispreferred that the acceptor has a bulk crushing strength above 10kg/cm². For this reason carrier materials based on reinforced refractoryoxides are very suitable. Such a refractory oxide may comprise alumina,silica, zirconia and thoria and/or mixtures of two or more of theseoxides. Silica-alumina, gamma-alumina and alpha-alumina are the mostpreferred carrier materials.

The copper or copper compound to be present on the carrier material isvery suitably applied on the carrier material by impregnation with asolution comprising a copper compound. Agueous solutions, in particularthose containing copper sulphate and/or copper nitrate, are preferred.In order to increase the capacity of the acceptors for the acceptance ofsulfur oxides it is of advantage to impregnate the carrier prior to orsimultaneously with the solution of a copper compound with a solution ofa compound of one or more of the metals zirconium, titanium, magnesiumand in particular aluminum. This capacity for acceptance of sulfuroxides is still further enhanced by impregnation of the carrier materialwith a solution of an alkali metal compound, in particular a sodiumsalt, simultaneously with or after impregnation with the afore-mentionedsolution of a compound or one or more of the metals zirconium, titanium,magnesium and aluminum. Very suitably the carrier is impregnated with asingle aqueous solution containing salts of copper, aluminum and sodium,e.g., as a nitrate or sulfate.

After impregnation the carriers loaded with the desired metal compoundsare dried and, if desired, heated to a temperature below 600°C, e.g., offrom 350°-550°C. The acceptor preferably contains copper oxide as thecopper compound. In cases where the calcination just mentioned does notlead to the formation of copper oxide (e.g., when the impregnation hasbeen carried out with sulfates), it is of advantage to convert thecopper compounds into the corresponding oxide by carrying out aprocedure similar to that for the regeneration of the loaded acceptor asdescribed below.

The amount of copper present in the acceptor very suitably ranges from1-10% by weight of the acceptor, preferably from 2-7% by weight.

The temperature during contact between the waste gas and the acceptor inthe first zone very suitably is in the range of from 300° to 500°C, withtemperatures as high as 430°C and as low as 325°C being preferred.During contact oxidative conditions must prevail. This is generallyaccomplished by the presence of oxygen, which in most cases is presentin the waste gases to be treated or otherwise may be provided by theaddition of, e.g., air.

The waste gases which have been freed from particulate matter and sulfuroxides may be carried off through a stack.

The acceptor which is loaded after contact with the waste gas in thefirst zone with particulate matter and with sulfur oxides is removedfrom that zone. According to the invention it has been found verydesirable to remove particulate material and the sulfur oxides from theloaded acceptor in separate zones. Although it is possible to remove thesulfur oxides before the particulate matter, it is preferred to free theacceptor of particulate matter first. According to the invention theremoval of particulate matter can very effectively be accomplished bystripping the acceptor in a second zone with an inert gas, in particularsteam. The particulate matter, which has smaller dimensions that theacceptor particles, is separated from the acceptor and is transported bythe inert gas. To take maximum advantage of this size differentiationand to thereby achieve optimum separation of the acceptor particles fromthe particulate matter it is advantageous to interpose a barriersubstantially impenetrable to the acceptor particles (because of theirsize) in the particulate matter removal zone through which theparticulate matter carried by the inert gas can pass after initialseparation is effected. To achieve this result under practicalconditions, this stripping is very suitably carry out by transportionthe loaded acceptor in relatively thin layers over perforated plates,and passing the inert gas through the acceptor layers via theperforations of the said plates. The perforated plates may be positionedunder a slope such that the acceptor moves over the said plates by meansof gravitational force.

The particulate matter can ultimately wholly or partly be separated fromthe inert gas (or after condensation from water in cases where steam isemployed) by conventional means, e.g., with the aid of filters or withone or more cyclones and or hydrocyclones.

The sulfur oxides still bound to the acceptor after the removal of theparticulate matter are removed from the acceptor material in a nextzone. This regeneration step is carried out by contacting the acceptorwith a suitable reducing gas such as hydrogen or hydrogen/carbonmonoxide mixtures, and hydrocarbon or mixtures of hydrocarbons.Preferably, the reducing gas comprising hydrogen is diluted with one ormore inert gases chosen from the group consisting of steam, nitrogen andcarbon dioxide. Very suitable diluted reducing gases are gases producedby the reaction of steam and methane, or gases obtained by the partialoxidation of hydrocarbons, or off-gases emanating from a catalyticreformer.

It is preferred that the molar ratio of the inert gas and combustiblecompounds in the reducing gas (in general hydrogen and/or carbonmonoxide and/or hydrocarbons) is from 3 to 10, preferably from 4 to 5. Apreferred inert diluent is steam.

The acceptor may be transported through the regeneration zone by anysuitable means, such as with the aid of bucket elevators, screwconveyors or vibrating conveyors. Since the reaction between the sulfuroxides-loaded acceptor and the reducing gas to release free sulfurdioxide is very rapid, in many cases all sulfur oxide is removed fromthe acceptor after a few seconds of contact with the reducing gas. Itis, therefore, preferred that the third zone comprises a riser tubedebouching into a cyclone through which zone the acceptor is transportedby means of the reducing gas. In this case the vertical riser tubefunctions both as a means for transporting the acceptor and as the zonefor the removal of sulfur oxides from the acceptor. In cases there theremoval of sulfur oxides from the acceptor in the said riser or othermeans of transport is not sufficient, a moving bed reactor may beinserted for the removal of the sulfur oxides from the loaded acceptorwith the aid of a reducing gas.

After the removal of the sulfur oxides, the reducing gas and theacceptor, are separated from each other by conventional gas-solidsphysical separation techniques. Preferably, this separation occurs inthe cyclone. In the cyclone the acceptor is kept in contact with thereducing gas, to ensure complete removal of sulfur oxides from theacceptor.

During the removal of the sulfur oxides from the acceptor with areducing gas, the temperature is very suitably in the range of from300°-500°C and preferably between 325°-475°C. The sulfur compoundsemerging from the acceptor are virtually completely in the form ofsulfur dioxide.

The reducing gas which has been in contact with the acceptor nowcontains the sulfur originally present in the waste gases in the form ofsulfur dioxide, and may have lost its reducing properties. This gas isremoved from the regeneration zone, and the sulfur dioxide presenttherein can be recovered by conventional means. It may be furtherprocessed by known methods to products, such as elemental sulfur,sulfuric acid or gypsum.

As the process of the invention is non-cyclic one, the gas emanatingfrom the regeneration zone will always have substantially the sameconcentration of sulfur dioxide. Therefore, this gas may conveniently bedirectly used for a process in which sulfur dioxide is converted intoother products (e.g., into elemental sulfur in a Claus plant). This isan important advantage of the present process over known cyclicprocesses wherein the concentration of sulfur dioxide in theregeneration off-gas, in general, varies in time. Costly installations,such as absorbers and strippers, are needed in these latter processes tocompensate for the fluctuations in the SO² -concentration in order tobring the sulfur dioxide from such a regeneration off-gas in a formsuited for further processing.

After removal of the sulfur oxides it is desirable to free the acceptorfrom any residual reducing gas before it is reintroduced into the sulfuroxide and particulate matter removal zone or before it is reactivatedwith an oxidizing agent according to the procedure described below. Thiscan be readily accomplished by stripping the acceptor with inert gas. Tothis end the acceptor is very suitably transported in relatively thinlayers over perforated plates and stripped with an inert gas which ispassed through the acceptor layers via the perforations in the plates.Preferably, the perforated plates are positioned at a slope fromhorizontal, with the acceptor being moved over the sloped plates bymeans of gravitational force. Steam is preferred as inert stripping gas.

The acceptor from which the sulfur oxides have at least partly, an inmost cases substantially completely been removed, may be recycled to thesulfur oxides and particulate matter removal (first) zone withoutreactivation. In an active acceptor the copper is, preferably, presentas its oxide. After treatment with the reducing gas the acceptorcontains the copper at least partly in the metallic form. When theacceptor in this form is used in the first zone the metallic copper isconverted into copper oxide by the oxidizing gas present in the saidfirst zone. However, since heat is liberated during the oxidation ofcopper to its oxide, an undesired rise in temperature may take place inthe first zone.

For this reason it is preferred to reactivate the acceptor in a separatezone before its introduction into the first zone. In this separate zonefor activation the acceptor is suitably contacted with an oxidizingagent, e.g., an oxygen-containing gas, such as air. In order to achievereactivation the acceptor may be transported through this separate zonevia any conventional technique for moving solid particles, e.g., bucketelevators, screw conveyors vibrating conveyors. It is preferred toreactivate the acceptor by contacting it with an oxygen-containing gasin a zone comprising a riser tube debouching into a cyclone. In thispreferred procedure the acceptor is transported through the activationzone by means of the oxygen-containing gas used for its reactivation.During transport through the vertical riser tube oxidation of the metalspresent on the carrier material takes place. The temperature duringtransport should, preferably, be kept within the temperature range ofthe subsequent cross-current contacting step in the first zone butduring oxidation of the metallic copper it may locally rise to atemperature beyond this range.

In the preferred embodiment of the invention relating to thereactivation zone the acceptor is separated from the oxidizing agent bythe cyclone and recycled to the first zone by any suitable means, e.g.,under the influence of gravitational force or by means of a conveyor.The remnant of the oxidizing agent (e.g., air) may be discharged to thestack, or be used for any other purpose, e.g., as part of the inlet airto the furnace from which the waste gases emerge.

The invention also relates to an apparatus particularly suited forcarrying out the process according to the invention. The apparatuscomprises a vessel for cross-current contacting of the waste gas with amoving bed of acceptor for sulfur oxides, and separate processingchambers for removal of the particulate matter from the loaded acceptor,for the removal of sulfur oxides for the loaded acceptor, and forreactivating the acceptor.

In a preferred embodiment the apparatus comprises:

A. a contacting vessel having an inlet for waste gases containing sulfuroxides and particulate matter and an outlet for waste gas substantiallyfree of sulfur oxides and particulate matter, an internal compartmentcontaining a moving bed of supported, copper-containing acceptor forsulfur oxides, said internal compartment being defined by perforatedwalls disposed inside the contacting vessel, an inlet for freshsupported copper-containing acceptor in fluid communication with saidinternal compartment and an outlet for said acceptor loaded with sulfuroxides and particulate matter also in fluid communication with saidinternal compartment, and a means for directing the flow of said wastegases and said moving bed of acceptor cross-currently to one another,said waste gas flowing through the perforated walls of said internalcompartment containing said moving bed of acceptor;

B. a first purge vessel for removing particulate matter from theacceptor with a bottom inlet for purge gas and a top outlet for purgegas and particulate matter, a top inlet for acceptor material loadedwith sulfur oxides and particulate matter connected to a loaded acceptoroutlet of said contacting vessel and a bottom outlet for purged acceptormaterial, at least one perforated plate disposed in the vessel at anangle with the vertical for transporting the loaded acceptor materialfrom its inlet to the outlet and a means for passing said purge gasthrough said perforated plate thereby stripping said particulate matterfrom said loaded acceptor during its transport on said perforated plate;

C. a first vertical riser tube debouching into a cyclone for removingsulfur oxides from the acceptor, having a bottom inlet for purgedacceptor material connected to the bottom outlet of the above purgevessel and a bottom inlet for reducing gas, a cyclone top outlet forsulfur oxide-containing gas and a cyclone bottom outlet for reducedacceptor material;

D. a second purge vessel with a bottom inlet and a top outlet for purgegas, a top inlet for reduced acceptor material connected to the abovecyclone bottom outlet and a bottom outlet for purged acceptor materealand at least one perforated plate disposed in the vessel at an anglewith the vertical for transporting acceptor material from its inlet tothe outlet, and

E. a second vertical riser tube debouching into a cyclone forreactivating the acceptor having a bottom inlet for purged acceptormaterial connected to the bottom outlet of the second purge vessel and abottom inlet for an oxygen-containing gas, a cyclone top outlet for theoxygen-containing gas and a cyclone bottom outlet for reactivatedacceptor material connected to the acceptor inlet of the abovecontacting vessel.

A schematical drawing of such an apparatus is given in FIG. 1. For thesake of simplicity auxiliary equipment, such as bolts, nuts, valves,heating and cooling equipment is not shown.

Flue gas is introduced via line 1 into cross-current contacting vessel2. The acceptor is fed to vessel 2 through line 3. The acceptor ispassed through the vessel and removed therefrom via line 4. The wastegas, which was in cross-current contact with the acceptor in vessel 2 isremoved therefrom via line 5, and may be led to the stack. In general,it may be partly cooled by heat transfer to air to be used forcombustion in the furnace from which the off-gas emerges. The acceptorremoved from the cross-current contacting vessel via line 4 is led to avessel 6, which is provided with perforated plates 7 at a slight anglewith the horizontal. The acceptor passes over the plates 7 bygravitational force, and the fly ash present thereon is removed with theaid of steam introduced via line 8. The fly ash is transported by thesteam via line 9 to a cyclone 10. From this cyclone dry fly ash isremoved through line 11, and a slurry of fly ash in water via line 12.The acceptor is removed via line 13 from vessel 6 to a riser 14. Vialine 15 a reducing gas (for example, a mixture of steam and hydrogen) isintroduced into riser 14, and the acceptor may be transported to cyclone16. In riser 14 the SO₂ is removed from the acceptor. From cyclone 16the gas, which now contains appreciable amounts of SO₂, is removed vialine 17. The acceptor is removed from cyclone 16 via line 18 to vessel19 equipped with perforated plates 20, which are at a slight angle withthe horizontal. Steam is introduced into vessel 19 via line 21, and thissteam, after having been in contact with the acceptor (which may passover plates 20 by gravitational force) is removed via line 22 fromvessel 19. Line 22 may be connected with line 17. The acceptor leavesvessel 19 through line 23 to a riser 24. Air is introduced into line 24via line 25, and the acceptor is led to a cyclone 26 via line 24. Inline 24 copper on the acceptor is oxidized to copper oxide.

From cyclone 26 the gas is removed via line 27. It may be used as feedair for the furnace from which the waste gas emerges, or it is passed tostack. The acceptor is recycled from cyclone 26 to reactor 2 via line 3.

The vessel in which the waste gas is to be contacted with the acceptor(vessel 2 in FIG. 1) may be constructed in several ways. The acceptor isto be transported through the vessel as a moving bed while beingcontacted cross-currently with the waste gas.

Two vessel or reactor types, which are very suitable for this purposeare shown schematically in FIGS. 2, 3 and 4, 5, respectively. FIG. 2shows a longitudinal section and FIG. 3 a perspective fuel of aso-called cylindrical radial flow reactor.

Acceptor material enters the reactor via the top nozzle 31 and isdistributed via conduits 32 into a cylindrical compartment 33 withperforated walls. On its flow downwards the acceptor is exposed to theflue gas. At the bottom of the cylindrical compartment the acceptor isremoved via conduit 34 and removed from the reactor via bottom nozzle35. The flue gas is passed from the reactor inlet 36 and via spacesbetween the conduits 34 into the central cone. From there is radiallypasses the acceptor layer present in the cylindrical compartment 33,thereby establishing the desired cross-current contact between movingacceptor particles and the waste gas. The flue gas stream at the top ofthe reactor via outlet 37.

It will be understood that several other embodiments of a cylindricalradial flow reactor are possible. I may, e.g., contain severalconcentrically arranged cylindrical compartments with perforated wallsthrough which the acceptor material is transported. In all cases theflue gases are introduced in such a way that they must at least passthrough one layer of acceptor material present in a cylindricalcompartment before leaving the reactor.

In FIGS. 4 and 5, a so-called parallel plate reactor is shown. FIG. 4 isa side view and FIG. 5 is a top view.

The acceptor material is fed to the top of the reactor by a hopper 41and distributed at the top over a number of compartments 42 arranged inparallel (e.g., by means of a closed channel-type conveyor 43). Theacceptor flows downwards through the compartments. The number ofcompartments and their size depend on the amount of flue gas to betreated, its width and on the allowable pressure drop. The side walls 44of the compartments are perforated to allow for passage of the flue gas.Both top and bottom parts of the compartments are, preferably,triangular in cross-section to get an equal distribution of acceptoracross the square cross area. Each compartment is equipped with a vanefeeder 45 at the bottom for withdrawal of loaded acceptor. At the bottomthe acceptor is collected using the same equipment as for thedistribution at the top. The flue gas enters the reactor horizontallyvia inlets 46 and is fed into flue gas inlet chambers 47. From here itpasses the acceptor layer and leaves the reactor via the flue gas outletchambers 48. Inlet and outlet chambers are arranged alternatively. Bothside walls of each chamber (excluding the first and the last one) areperforated. The distribution of the flue gas across the reactor sectionis obtained by one or more pyramidical inlet and outlet devices 49. Theoutlet system is identical to the inlet device.

EXAMPLE

Flue gas of 250 MW boiler amounting to 783,000 Nm³ /h gas containing0.16% vol. SO₂ and 8.7 g Nm³ fly ash, is introduced at the bottom of abi-cylindrical radial flow reactor, as described above, with a diameterof 12 meters at a temperature of 400°C and about atmospheric pressure.The layer thickness of the acceptor in each cylindrical compartment is50 cm and the acceptor moves through the compartment by gravitationalforce at a rate of about 1 mm/sec. The acceptor consists of reinforcedalumina comprising 5%wt of copper. Its bulk density is 1100 kg/m³ andits size 3-5 mm. After passage through the two cylindrical compartmentscross-currently to the moving acceptor, the purified flue gas leaves thereactor at its top. The flue gas particulate matter is reduced to 0.09g/Nm³ and its SO₂ content is 160 ppm vol. After leaving thebi-cylindrical radial flow reactor the acceptor is freed fromparticulate matter by stripping with low pressure steam in a purgevessel comprising three inclined perforated trays. The temperatureduring stripping is 390°C and the pressure is slightly above atmosphericpressure. The acceptor is introduced at the top of the purge vessel andleaves it at the bottom. A gas stream of steam and particulate matterleaves the purge vessel at its top. The acceptor now free fromcontaminating particulate matter is then introduced in a riser tube withan inside diameter of 1.0 meter in which it is contacted with a reducinggas comprising 15%vol. H₂ and introduced in the said riser rube at arate of 15,000 kg/h. The riser debouches into a cyclone with a diameterof 2.5 m wherein acceptor and reducing gas are separated. The acceptorleaves the cyclone at its bottom and is introduced into a second purgevessel which is similar to the one described above. The conditionsduring stripping with steam are almost identical, i.e., 380°C and apressure of about 1.0 kg/cm² abs. The acceptor is subsequentlyintroduced in a second riser (diameter: 0.65 m) in which it is treatedwith air in order to oxidize its metallic copper to copper oxide. Air isintroduced at a temperature of 30°C and at a rate of 13,500 kg/h. Duringthe oxidation step the acceptor temperature rises to 410°C. Air andoxidized acceptor are separated from each other in a cyclone into whichthe second riser debouches. The diameter of this cyclone is 2.0 m. Fromthe latter cyclone regenerated and reactivated acceptor is recycled tothe top of the bi-cylindrical radial flow reactor.

What is claimed is:
 1. A process for removing sulfur oxides andparticulate matter from waste gas streams containing sulfur oxides andparticulate matter which comprises:A. contacting the waste gas streamunder oxidative conditions in a sulfur oxide and particulate matterremoval zone with a solid acceptor comprising copper or a coppercompound or mixtures thereof supported on a particulate carrier, saidcontact being established by passing the waste gas at a temperature offrom about 300° to 500°C. cross-currently through a moving bed of thesolid acceptor, thereby accepting the sulfur oxide on said acceptor andfiltering out the particulate matter to afford an acceptor loaded withsulfur oxides and particulate matter and a waste gas streamsubstantially free of both sulfur oxides and particulate matter; B.removing the particulate matter from the loaded acceptor in a firstseparation zone wherein the acceptor loaded with both sulfur oxides andparticulate matter is stripped of particulate matter by transporting theloaded acceptor through a stream of an inert stripping gas; C.separating the sulfur oxides from the acceptor product of the firstseparation zone by contacting the acceptor with a reducing gas at atemperature between 300°-500°C in a second separation zone whereby thesulfur oxides bound to the acceptor are released as SO₂ gas and D.returning the acceptor product of the second separation zone intocross-current contact with said waste gases under oxidative conditionsin the sulfur oxide and particulate matter removal zone.
 2. The processaccording to claim 1, wherein the removal of particulate matter from theloaded acceptor in the first separation zone is effected by transportingthe acceptor in relatively thin layers over the perforated plates and bypassing the inert gas through the acceptor layers via the perforationsof the said plates.
 3. The process according to claim 2 wherein theperforated plates are positioned under a slope from horizontal and theacceptor moves over the plate by means of gravitational forces.
 4. Theprocess according to claim 1 wherein the acceptor product of the secondseparation zone is reactivated by contacting it with an oxidizing agentin an activation zone prior to introducing said acceptor into the sulfuroxide and particulate matter removal zone.
 5. The process according toclaim 4 wherein the oxidizing agent employed is an oxygen-containinggas.
 6. The process according to claim 1 wherein the thickness of themoving bed of acceptor particles in cross-current contact with the wastegas stream in the sulfur oxide and particulate matter removal zone isbetween about 25 and 100 cm taken in the direction of waste gas flow. 7.The process according to claim 6 wherein the velocities of the waste gasstream and the moving bed in cross-current contact are between about 1and 7 m/sec and from about 0.4 to about 2.5 mm/sec, respectively.
 8. Theprocess according to claim 1 wherein the acceptor product of the secondseparation zone is stripped with an inert gas prior to being returnedinto cross-current contact with the waste gases under oxidativeconditions in the sulfur oxide and particulate matter romoval zone. 9.The process according to claim 8 wherein the inert gas stripping of theacceptor product of the second separation zone is carried out bytransporting the acceptor in relatively thin layers over perforatedplates and by passing the inert gas through the acceptor layers via theperforations of the said plates.
 10. The process according to claim 9wherein the perforated plates are positioned under a slope fromhorizontal and the acceptor moves over the plate by means ofgravitational force.